THE QUALITY OF WHEAT
In discussing the quality of wheat it is necessary to adopt two
distinct points of view, that of the farmer and that of the miller. A
good wheat from the farmer’s point, of view is one that will year by
year give him a good monetary return per acre. Now the monetary return
obviously depends on two factors, the yield per acre and the value per
quarter, coomb, or bushel, as the case may be. These two factors are
quite independent and must be discussed separately.
We will first confine our attention to the yield per acre. This has
already been shown to depend on the presence in the soil of plenty of
the various elements required by plants, in the case of wheat nitrogen
being especially important. The need of suitable soil and proper
cultivation has also been emphasised. These conditions are to a great
extent under the control of the farmer, whose fault it is if they
are not efficiently arranged. But there are other factors affecting
the yield of wheat which cannot be controlled, such for instance as
sunshine and rainfall. The variations in these conditions from year to
year are little understood, but they are now the subject of accurate
study, and already Dr W. N. Shaw, the chief of the Meteorological
Office has suggested a periodicity in the yield of wheat, connected
with certain climatic conditions, notably the autumnal rainfall.
We have left to the last one of the most important factors which
determine the yield of wheat, namely, the choice of the particular
variety which is sown. This is undoubtedly one of the most important
points in wheat-growing which the farmer has to decide for himself.
The British farmer has no equal as a producer of high class stock. He
supplies pedigree animals of all kinds to the farmers of all other
lands, and he has attained this preeminence by careful attention to
the great, indeed the surpassing, importance of purity of breed. It
is only in recent years that the idea has dawned on the agricultural
community that breed is just as important in plants as in animals. It
is extraordinary that such an obvious fact should have been ignored
for so long. That it now occupies so prominently the attention of the
farmers is due to the work of the agricultural colleges and experiment
stations in Sweden, America, and many other countries, and last but
by no means least in Great Britain. This demonstration of the value
of plant breeding is perhaps the greatest achievement in the domain
of agricultural science since the publication of Lawes and Gilbert’s
classical papers on the manurial requirements of crops.
Wheat is not only one of the most adaptable of plants. It is also one
of the most plastic and prone to variation. During the many centuries
over which its cultivation has extended it has yielded hundreds of
different varieties, whose origin, however, except in a few doubtful
cases is unknown. Comparatively few of these varieties are in common
use in this country, and even of these it was impossible until recently
to say which was the best. It was even almost impossible to obtain
a pure stock of many of the standard varieties. This is by no means
the simple matter it appears to be. It is of course quite easy to pick
out a single ear, to rub out the grain from it, to sow the grain on a
small plot by itself and to raise a pound or so of perfectly pure seed.
This can again be sown by itself, and the produce, thrashed by hand,
will give perhaps a bushel of seed which will be quite pure. From this
seed it will be possible to sow something like an acre; and now the
trouble begins. Any kind of hand thrashing is extremely tedious for the
produce of acre plots, and thrashing by machinery becomes imperative.
Now a thrashing machine is an extremely complicated piece of apparatus,
which it is practically impossible thoroughly to clean. When once seed
has been through such a machine it is impossible to guarantee its
purity. Contamination in the thrashing machine is usually the cause of
the impurity of the stocks of wheat and other cereals throughout the
country. The only remedy is for the farmer to renew his stock from time
to time from one or other of the seedsmen or institutions who make it
their business to keep on hand pure stocks obtained by the method above
described.
[Illustration: Fig. 1. Typical ears of a few of the many cultivated
varieties of wheat]
Comparative trials of pure stocks of many of the standard varieties
of wheat, and of the other cereals, are being carried out in almost
every county by members of the staff of the agricultural colleges.
The object of such trials is to determine the relative cropping power
of the different varieties. This might at first sight appear to be
an extremely simple matter, but a moment’s consideration shows that
this is not the case. No soil is so uniform that an experimenter can
guarantee that each of the varieties he is trying has the same chance
of making a good yield as far as soil is concerned. It is a matter of
common knowledge too that every crop of wheat is more or less affected
by insect and fungoid pests, whose injuries are unlikely to fall
equally on each of the varieties in any variety test. Many other causes
of variation, such as unequal distribution of manure, inequalities in
previous cropping of the land, irregular damage by birds, may well
interfere with the reliability of such field tests.
Much attention has been given to this subject during the last few
years, and it has been shown that as often as not two plots of the
same variety of wheat grown in the same field under conditions which
are made as uniform as possible will differ in yield by 5 per cent. or
more. Obviously it is impossible to make comparisons of the cropping
power of different varieties of wheat as the result of trials in
which single plots of each variety are grown. It is a deplorable fact
however that the results of most of the trials which are published are
based on single plots only of the varieties compared. Such results
can have no claim to reliability. Single plots tests are excellent
as local demonstrations, to give the farmers a chance of seeing the
general characters of the various wheats in the field, but for the
determination of cropping power their results are misleading. For
the comparison of two varieties however an accuracy of about 1 per
cent., which is good enough for the purpose in view, can be obtained
by growing, harvesting and weighing separately, five separate plots of
each variety under experiment, provided the plots are distributed in
pairs over the experimental field.
Still greater accuracy can be attained by growing very large numbers
of very small plots of each variety in a bird-proof enclosure. The
illustration shows such an enclosure at Cambridge where five varieties
were tested, each on 40 plots. Each plot was one square yard, and the
whole 200 plots occupied so small an area that uniformity of soil could
be secured by hand culture.
Several experimenters are now at work on these lines, and it is to be
hoped that all who wish to carry out variety tests will either follow
suit, or content themselves with using their single plots only for
demonstrating the general characters of the varieties in the field.
So far we have confined our discussion to the standard varieties, and
we must now turn our attention to the work which has been done in
recent years on the breeding of new varieties which will yield heavier
crops than any of the varieties hitherto in cultivation.
[Illustration: Fig. 2. Part of bird-proof enclosure containing many
small plots for variety testing]
It is impossible to give more than a very brief outline of the vast
amount of work which has been done on this subject. Broadly speaking,
two methods have been used, selection and hybridisation. Of these
selection is the simpler, but even selection is by no means the simple
matter it might appear to be. Let us examine for a moment the various
characters of a single wheat plant which determine its capacity for
yielding grain. The average weight of one grain, the number of grains
in an ear, the number of ears on the plant, are obviously all of them
characters which will influence the weight of grain yielded by the
plant. Many experimenters have examined thousands of plants for these
characters, often by means of extremely ingenious mechanical sorting
instruments, and have raised strains of seed from the plants showing
one or more of these characters in the highest degree. The results of
this method of selection have as a rule been unsuccessful, no doubt
because the size of the grain, the number of grains in the ear, and
the number of ears on the plant, are so largely determined by the food
supply, or by some other cause quite outside the plant itself. They are
in fact in most cases acquired characters, and are not inherited. This
method of selection results in picking out rather the well nourished
plant than the well bred one. Again it is obvious that the weight of
grain per acre is measured by the weight of one grain, multiplied by
the number of grains per ear, multiplied by the number of ears per
plant, multiplied by the number of plants per acre. Selecting for any
one of these characters, say large ears, is quite likely to diminish
other equally important characters, say number of ears per plant.
In order to avoid these difficulties the method of selection according
to progeny has been devised. The essence of this method is to select
for stock, not the best individual plant, but the plant whose progeny
yields the greatest weight of seed per unit area. This method was
applied with great industry and some success in the Minnesota wheat
breeding experiments of Willett Hays. Large numbers of promising plants
were collected from a plot of the best variety in that district. The
seed from each plant was rubbed out and sown separately. One hundred
seeds from each plant were sown on small separate plots which were
carefully marked out and labelled. Every possible precaution was taken
to make all the little plots uniform in every way. By harvesting each
plot separately, and weighing the grain it produced, it was possible to
find out which of the original plants had given the largest yield. This
process was repeated by sowing again on separate plots a hundred seeds
from each individual plant from the best plot, and again weighing the
produce of each plot. After several repetitions it was stated that new
strains were obtained which yielded considerably greater crops than the
variety from which they were originally selected. These results were
published in 1895, but no definite statements have since appeared as to
the success ultimately attained.
This method of selection is undoubtedly more likely to give successful
results than the method which depends on the selection of plants for
their apparent good qualities; but it has several weak points. In
the first place it is almost impossible to make the soil of a large
number of plots so uniform that variation in yield due to varying soil
conditions will not mask the variations due to the different cropping
power of the seed of the separate plants. Many experimenters are still
at work with a view to overcome this difficulty. Secondly, plant
breeders are by no means agreed on the exact theoretical meaning of
improvement by selection. The balance of evidence at the present time
seems to tend towards the general adoption of what is known as the
pure-line theory. According to this theory, which was first enunciated
by Johannsen of Copenhagen as the outcome of a lengthy series of
experiments with beans, the general population of plants, in say a
field of wheat of one of the standard varieties giving an average
yield of say 40 bushels per acre, consists of a very large number of
races each varying in yielding capacity from say 30 to 50 bushels per
acre. These races can be separated by collecting a very large number
of separate plants, sowing say 100 seeds from each on a separate plot,
and weighing the produce separately. The crop on each plot, being the
produce of a separate plant, will be a distinct race, or pure line
as it is called, and each pure line will possess a definite yielding
power of its own. If this is so the difficulty of soil variation can be
overcome by saving seed from many of the best plots, and sowing it on
several separate plots. At harvest time these are gathered separately
and weighed. By averaging the weights of grain from many separate plots
scattered over the experimental area the effect of soil variation can
be eliminated.
The method is very laborious, but seems to promise successful results.
For instance, Beaven of Warminster, working on these lines, has
succeeded in isolating a pure line of Archer barley which is a distinct
advance on the ordinary stocks of that variety. There appears to be
no reason why it should not be applied to wheat with equal success;
in fact, Percival of Reading states that his selected Blue Cone wheat
was produced in this way. The essence, of the method is that if the
pure-line theory holds there is no necessity to continue selecting
the best individual plant from each plot, for each plot being the
produce of a single plant must be a pure line with its own definite
characters. The whole of the seed from a number of the best plots can
therefore be saved. The seed from each of these good plots can be used
to sow many separate plots: by averaging the yields from these plots
the effects of soil variation can be eliminated, and the cropping
power thus determined with great accuracy. It is thus possible to
pick out the best pure line with far greater certainty than in any
other way. It must not be forgotten, however, that the success of the
method depends on the truth of the pure-line theory. It should also
be pointed out that the cereals are all self-fertilised plants. When
working on these lines with plants which are readily cross-fertilised,
such for instance as turnips or mangels, it is necessary to enclose the
original individual plants, and the subsequent separate plots, so as to
prevent them from crossing with plants of other lines, in which case
the progeny would be cross-bred and not the progeny of a single plant.
This of course enormously increases the difficulty of carrying out the
experiment. Enough has been said to show that the task of improving
plants by systematic selection is an extremely tedious and difficult
one. Of course anyone may be fortunate enough to drop on a valuable
sport when carefully inspecting his crops, and it appears likely that
many of the most valuable varieties in cultivation have originated from
lucky chances of this kind.
It has always been the dream of the plant breeder to make use of the
process of hybridisation for creating new varieties, but until the
work of Mendel threw new light on the subject the odds were against
the success of the breeder. The idea of the older hybridisers was that
crossing two dissimilar varieties broke the type and gave rise to
greatly increased variation. From the very diverse progeny resulting
from the cross, likely individuals were picked out. Seed was saved from
these and sown on separate plots, and attempts were made to obtain a
fixed type by destroying, or roguing as it is called, all the plants
which departed from the desired type. This was a tedious process which
seldom resulted in success. Mendel’s discoveries, made originally
nearly 50 years ago, as the result of experiments in the garden of
his monastery, in the crossing of different varieties of garden peas,
remained unknown until rediscovered in 1899. In the 12 years which
have elapsed since that date the results which have been achieved show
clearly that the application of Mendelian methods is likely greatly
to increase the simplicity and the certainty of plant improvement by
hybridisation.
[Illustration: Fig. 3. A wheat flower with the chaff opened to show the
stamens and the stigmas]
Perhaps the best way of describing the bearing of Mendel’s Laws on the
improvement of wheat is to give an illustration from the work carried
out by Biffen at Cambridge, dealing at first with simple characters
obvious to anyone. In one of his first experiments two varieties of
wheat were crossed with each other. The one variety possessed long
loose beardless ears, the other short dense bearded ears. The crossing
was performed early in June, sometime before what the farmer calls
flowering time. The flowering of wheat as understood by the farmer
is the escape of the stamens from the flower. Fertilisation always
takes place before this, and crossing must be done of course before
self-fertilisation has been effected. The actual crossing is done
thus: An ear of one of the varieties having been chosen, one of the
flowers is exposed by opening the chaff which encloses it (Fig. 3),
the stamens are removed by forceps, and a stamen from a flower of the
other variety is inserted, care being taken that it bursts so that
the pollen may touch the feathery stigmas. The chaff is then pushed
back so that it may protect the flower from injury. The pollen grains
grow on the stigmas, and penetrate down the styles into the ovary. In
this way cross-fertilisation is effected. It is usual to operate on
several flowers on an ear in this way, and to remove the other flowers,
so that no mistake may be made as to which seed is the result of the
cross. Immediately after the operation the ear is usually tied up in
a waxed paper bag. This serves to make it absolutely certain that
no other pollen can get access to the stigmas except that which was
placed there. At the same time it is a convenient way of marking the
ear which was experimented upon. The cross is usually made both ways,
each variety being used both as pollen parent and as ovary parent.
As soon as the cross-fertilised seeds are ripe they are gathered, and
early in the autumn they are sown. It is almost necessary to sow them
and other small quantities of seed wheat in an enclosure protected by
wire netting. Otherwise they are very liable to suffer great damage
from sparrows. The plants which grow from the cross-fertilised seeds
are known as the first generation. In the case under consideration,
they were found to produce ears of medium length and denseness,
intermediate between the ears of the two parent varieties, and to be
beardless. The first generation plants were also characterised by
extraordinary vigour, as is the case with almost all first crosses,
both in plants and animals. Their seed was saved and sown on a small
plot, and produced some hundreds of plants of the second generation.
On examining these second generation plants it was found that the
characters of the parent varieties had rearranged themselves in every
possible combination, long ears with and without beard, short ears with
and without beard, intermediate ears with and without beard, as shown
in Fig. 4. These different types were sorted out and counted, when they
were found to be present in perfectly definite proportions. This is
best shown in the form of a tabulated statement, thus:
Ears Ears Ears Ears Ears Ears
Long Long Medium Medium Short Short
Beardless Bearded Beardless Bearded Beardless Bearded
3 1 6 2 3 1
Translating this into words, out of every 16 plants in the second
generation there were four long eared plants, three beardless and one
bearded; eight plants with ears of intermediate length, six beardless
and two bearded; and four short eared plants, three beardless and one
bearded. The illustration shows all these types. The experiment has
been repeated several times and the same proportions were invariably
obtained. The result, too, was independent of the way the cross was
made. Seed was collected separately from large numbers of single
plants of each type. The seed from each plant was sown by itself
in a row, so that its progeny could be separately observed. It was
found that all the plants of the second generation possessing ears of
intermediate length produced in the third generation plants with long
ears, short ears, and medium ears in the proportion of 1 : 1 : 2, the
same proportion in fact as in the second generation. Short eared plants
produced only short eared offspring, long eared plants only long eared
offspring. Bearded plants produced only bearded offspring. Beardless
plants, however, produced in some cases only beardless offspring, in
other cases both beardless and bearded offspring in the proportion of
three of the former to one of the latter. Out of every three beardless
plants only one was found to breed true, whilst two gave a mixed
progeny. It appears therefore that in the second generation some of the
types which occur breed true, whilst others do not. Some of the true
breeding individuals can be picked out at sight, for instance, those
with long or short bearded ears. Some of those which will not breed
true can also be recognised by inspection, for instance, all the plants
with ears of intermediate length. In other cases it is only possible to
pick out the individual plants which breed true by growing their seed
and observing how it behaves. If it produces progeny all of which are
like the plant from which the seed was obtained, that plant is a fixed
type and will breed true continuously in the future. The final result
of the experiment was to obtain in three years from the time the cross
was made, four fixed types which subsequent experience has shown breed
true continuously, a long eared bearded type, a short eared beardless
type, a long eared beardless type and a short eared bearded type. Of
these the second two are exactly like the two parental varieties, but
the first two are new, each combining one character from each parent.
These fixed types already existed in the second generation. Mendel’s
discoveries with peas showed how to pick them out. Obviously there is
no need for the years of roguing by which the older hybridisers used
to attempt to fix their desired type. All the types are present in the
second generation. Mendel has shown how the fixed ones may be picked
out.
[Illustration: Fig. 4. _P_, _P_, the two parental types. _F₁_ the first
cross. _F₂_, 1-6, the types found in the second generation]
The characters described above are not of any great economic
importance. Biffen has shown that such important characters as
baking strength and resistance to the disease known as yellow rust
behave on crossing in the same way as beard. Working on the lines of
the experiment described above he has succeeded in producing several
new varieties which in baking strength and in rust resistance are a
distinct advance on any varieties in cultivation in this country.
His method of working was to collect wheats from every part of the
world, to sow them and to pick out from the crop, which was usually
a mixed one, all the pure types he could. These were grown on small
plots for several years under close observation. Many were found to
be worthless and were soon discarded. Others were observed to possess
some one valuable character. Amongst these a pure strain of Red Fife
was obtained from Canadian seed, which was found to retain when grown
in England the excellent baking strength of the hard wheats of Canada
and North America. Again, other varieties were noticed to remain free
from yellow rust year after year, even when varieties on adjoining
plots were so badly infected that they failed to produce seed. Other
varieties, too, were preserved for the sturdiness of their straw,
their earliness in ripening, vigour of growth, or yielding capacity.
Many crosses were made with these as parents. The illustration shows
a corner of the Cambridge wheat-breeding enclosure including a
miscellaneous collection of parent varieties. The paper bags on the
ears show where crosses have been made. From the second generation
numbers of individual plants possessing desirable characters were
picked out, and the fixed types isolated in the third generation by
making cultures from the seed of these single plants. The seed from
these fixed types was sown on small field plots, at which stage many
had to be rejected because they were found wanting in some character
of great practical importance which did not make itself evident in
the breeding enclosure. The illustration shows a case in point. It
was photographed after heavy rain in July. The weakness of the straw
of the variety on the left had not been noticed in the enclosure. The
types which approved themselves on the small field plots were again
grown on larger plots so that their yield and milling and baking
characters could be tested. So far two types have survived the ordeal.
One combines the cropping power of the best English varieties with the
baking strength of North American hard wheat. It is the outcome of a
cross between Rough Chaff and Red Fife. Its average crop in 1911 was 38
bushels per acre as the result of 28 independent trials, and, where the
local millers have found out its quality, it makes on the market four
or five shillings per quarter more than the ordinary English varieties.
The other resulted from a cross between Square Head’s Master and
a rust-resisting type isolated from a graded Russian wheat called
Ghirka. It is practically rust-proof. Consequently it yields a heavier
crop than any of the ordinary varieties which are all more or less
susceptible to rust. The presence of rust in and on the leaves hinders
the growth of the plant, lowers the yield, and increases the proportion
of shrivelled grains. It has been estimated that rust diminishes the
world’s wheat crop by something like one third. The new rust-proof
variety gave an average yield of about 6 bushels per acre more than
ordinary varieties on the average of 28 trials last year. It is called
Little Joss and is especially valuable in the Fens and other districts
where rust is more than usually virulent.
[Illustration: Fig. 5. Corner of bird-proof enclosure showing a varied
assortment of parent varieties of wheat. Crosses have been made on some
of them as shown by the ears tied up in paper bags]
[Illustration:
Fig. 6. Field plots of two new varieties of the same parentage
which had approved themselves in the bird-proof enclosure. That
on the left had to be rejected on account of the weakness of
its straw. That on the right is the rust-proof variety known as
Little Joss. The photograph was taken after a storm which in
the open field found out the weak point of the one variety]